|MadSci Network: Engineering|
I do not understand your intentions and until you define them I can only give some basic ideas about electrical conduction. Electrical conduction requires motion of charged particles. In metallic conductors these are electrons in conduction bands. In non metallic solids, liquids and gases the charged particles are ions. Any material subjected to an appropriately large voltage can become a conductor. Materials that require a minimum of voltage,such as most metals are conductors; materials, such as air, most glasses,crystalline solids, plastics, organic materials, that require very high voltages are insulaters. Ignoring semiconductors [http://en.wikipedia.org/wiki/Semiconductor] there are materials that are intermediate in conduction; These are ionic compounds in which the ions are mobilized by either melting, such as molten silicate glasses or molten salts, or by dissolution in a polar solvent such as salts in water, or by dissociation as in the self protonation of water, alcohols, ammonia, or the disassociation of strong and weak acids in polar solvents such as water. Conduction of ions in solution has 5 requirements: 1. mobile ions in solution; 2. a site for oxidation [anode] and a site for reduction [cathode]; 3. a cathode half reaction and an anode half reaction. 4. a conductive pathway between the anode and cathode sites; and 5. an electrical potential difference between the anode and cathode. If one is lacking conduction ceases. The electrical potential can be chemical for galvanic reactions or imposed by an electric current for electrolytic reactions. This is explained in the following reference and in many chemistry texts. corrosion: http://www.tech.plym.ac.uk/sme/strc201/corrosion1.htm Water would be an excellent insulator except for its self ionization into hydronium [H3O+] and hydroxide [OH-] ions that are present in even the purest water; add common contaminants and water is a fairly good conductor. Most fairly simple electrical devices that are scrupulously cleaned of ionic contaminants will operate for a short while if placed in high quality deionized water. But under the voltages present corrosion slowly occurs, ions build up, alternate electrical pathways develop, and the device fails, sometimes quite dramatically. The above reference lists some common galvanic potentials, check it out, and they are all under about 5 volts so electrolytic reactions don't need much voltage to happen, anything over fractions of a volt can cause something to happen. So the normal approach to protect against electrolytic failure is to remove the ionic pathway by good insulation and encapsulation or by sealing the device or submerging in an insulating fluid. I think PCBs were used for that. Of course there is another approach and we are fortunate in that each of us has a [usually] fully functioning computer that operates submerged in water OUR BRAIN. I am not really knowledgeable in its function but we can intuit several things 1. it operates at very low voltages, The cathode and anode reactions are tuned to operate at these voltages and probably rely on monitoring the electrolyte concentrations as switches, there must be appropriate ion permeable membranes to control the electrical potentials, the presence of contaminants must be strictly controlled for proper operation. There are plenty more so read up on it. http://www.fi.edu/learn/brain/stress.html Back to your idea of conductive plastics in water. the usual failure mode is electrochemical destruction of a metal conductor and formation of metallic conductive pathways between areas of differing voltage. Plastic conductors would eliminate this by removing anode and cathode reactions. Conductive polymers tend to be only fair conductors so any reasonable answer would probably be in the nanotechnology carbon nanotube area. The device would have to be massively parallel and highly integrated. Here is an idea of what is happening. Go on the web and to the library and see what can be done and make a simple prototype.
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/9639/30463/01404205.pdf?temp=x Happy inventing, JimG
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